A formal model for reasoning about adaptive QoS-enabled middleware

Systems that provide distributed multimedia services are subject to constant evolution; customizable middleware is required to effectively manage this change. Middleware services for resource management execute concurrently with each other, and with application activities, and can, therefore, potentially interfere with each other. To ensure cost-effective QoS in distributed multimedia systems, safe composability of resource management services is essential. In this article, we present a meta-architectural framework, the Two-Level Actor Model (TLAM) for customizable QoS-based middleware, based on the actor model of concurrent active objects. Using TLAM, a semantic model for specifying and reasoning about components of open distributed systems, we show how a QoS brokerage service can be used to coordinate multimedia resource management services in a safe, flexible, and efficient manner. In particular, we show a system in which the multimedia actor behaviors satisfy the specified requirements and provide the required multimedia service. The behavior specification leaves open the possibility of a variety of algorithms for resource management. Furthermore, constraints are identified that are sufficient to guarantee noninterference among the multiple broker resource management services, as well as providing guidelines for the safe composition of additional services.